The present invention relates to a method for overlaying a copper type alloy material as padding material, and more particularly relates to such a method for overlaying a copper type alloy material as padding material upon a substratum of an aluminum type base metal such as aluminum alloy.
The present invention has been described in Japanese Patent Application Serial No. Showa 60-157622 (1985), filed by an applicant the same as the entity assigned or owed duty of assignment of the present patent application; and the present patent application hereby incorporates into itself by reference the text of said Japanese Patent Application and the claim and the drawings thereof; a copy is appended to the present application.
Aluminum type materials such as aluminum alloys are light, having specific gravities approximately one third of iron, and in many fields of art advantage is taken of this lightness by utilizing aluminum type materials in parts, such as automobile and airplane parts. However, the melting point of aluminum type materials such as aluminum alloys is relatively low, being approximately 660.degree. C. at maximum, and accordingly it is not possible to utilize such aluminum type materials such as aluminum alloys for uses which require high thermal resistance. A further problem is that, because these aluminum type materials such as aluminum alloys are generally softer than iron, it is not possible to utilize such materials for uses which have a high abrasion resistance requirement.
Therefore, in order to utilize such aluminum type materials such as aluminum alloys in parts which are required to have good thermal resistance or high abrasion resistance, methods have been advanced according to which layers of materials with superior thermal resistance and abrasion resistance characteristics are joined to or overlaid upon a base of such an aluminum type material such as an aluminum alloy.
Prior art type such methods relating to aluminum type materials such as an aluminum alloys include, among others: (a) resistance welding (spot welding, seam welding, or the like); (b) argon arc welding; and (c) brazing (so called padding). Of these methods, resistance welding and argon arc welding are predicated on the melting of the base aluminum type material such as aluminum alloy. In the earlier history of the art, resistance welding was virtually exclusively employed; however, recently argon arc welding has been introduced. However, the following problems have been experienced with the welding of aluminum type materials such as aluminum alloys:
(1) Aluminum type materials such as aluminum alloys oxidize extremely quickly and easily when subjected to high temperatures, and typically create alumina of relatively high melting point, circa 2700.degree. C. This alumina creates severe handicap to the fusion of the joining portion between the aluminum type material such as aluminum alloy and the overlaid material, and its existence as an impurity in said joining portion causes a deterioration in the strength of the join.
(2) Eliminating the alumina produced as described above in (1) is not easy, and, when a solvent is used for such elimination, a further problem arises in that the solvent must be itself eliminated subsequent to the elimination of the alumina.
(3) Since the thermal conductivity of aluminum type materials such as aluminum alloys is relatively high, it is difficult to concentrate the heat and to effect local heating for welding. Moreover, once the material begins to melt, it melts over a relatively wide area and volume, and adjusting the speed of the welding process becomes difficult.
(4) Because the coefficient of thermal expansion of aluminum type materials such as aluminum alloys is relatively high, the occurrence of cracks and warping is quite likely.
(5) While in the molten condition, aluminum type materials such as aluminum alloys readily absorb hydrogen and/or water vapor, and accordingly a large degreee of gas flawing inevitably occurs.
There arise, therefore, many problems in the welding of such aluminum type materials such as aluminum alloys, and previously it has been virtually impracticable to provide the joining portion between the aluminum type material such as aluminum alloy and the material overlaid thereon with sufficient abrasion resistance characteristic and to treat the same as a functional material. In other words, in treating said joining portion between the aluminum type material such as aluminum alloy and the material overlaid thereon as a functional material, the material composition of said joining portion is extremely important, but in the case of the processes (a) and (b) detailed above the melting and penetration of the aluminum type material such as aluminum alloy is inevitable and indeed is a precondition for the process, and hence the joining portion is composed of an alloy of the overlaid material and the aluminum type material such as aluminum alloy. This alloy layer is inevitably deficient with regard to abrasion resistance and strength in the high temperature region, and hence it can only be utilized in an extremely limited temperature range, for example below about 100.degree. C. Up till the present, it has been considered that this state of affairs is quite natural.
Considering now the case (c) of brazing, although this process is also to some extent subject to the problems outlined in (1) through (5) above, on the other hand brazing does have the advantage that dissimilar materials with dissimilar abrasion, thermal, and corrosion resistance properties can be satisfactorily joined together, without the necessary loss of such properties. However, although brazing does enable the joining together of such dissimilar materials, at least one thereof having superior abrasion resistance and other characteristics, there are problems related to brazing when it is used as a joining process. In other words, because it is a precondition that the aluminum type material such as aluminum alloy utilized as a base material should not be very substantially melted, it has so far been commonly understood that the material utilized for the brazing of a dissimilar material to an aluminum type material such as aluminum alloy should have a melting point very close to or below the melting point of aluminum. As an example even brazing solder as used in the brazing of aluminum type base materials such as aluminum alloys has a comparatively high melting point such as approximately 50.degree. C. higher than aluminum. Accordingly, the use of Ni solder, which has a melting point of roughly 1000.degree. C., is absolutely inconceivable. As a result, even if a dissimilar material of superior thermal resistance, abrasion resistance, and corrosion resistance is joined to the aluminum type material such as aluminum alloy, since the melting point of the brazing solder utilized is relatively low, it has been impossible for the reasons set forth in (a) and (b) above to use the product manufactured in such a manner as a functional material for high temperature applications.
Moreover, considering the brazing or padding of aluminum type materials such as aluminum alloys from the viewpoint of said aluminum type materials, it becomes apparent that materials of high plasticity have comparatively favorable brazability, while on the other hand cast materials and die cast materials have extremely poor brazability. According to this, in the past, brazing has been very difficult.